Recovery of basic copper sulphate from rayon manufacture



Patented July 9, 1940 PATENT j OFFICE RECOVERY oF BAsIo COPPER SUIQPHATEFROM RAYON MANUFACTURE Sverre; Gulbrandsen, Woodbury, N. J., assignor toNew Process Rayon, Ina, Gloucester, N. J.,

a corporation of Delaware No Drawing. Application May 21, 1938,

Serial No. 209,366

17 Claims. o1..lzs+125) My invention consists in a process of producingbasic copper sulphate and ultimately copper hydroxide, from the dilutewaste acid liquor derived from the treatment of coagulated fibre of thecupro-ammonium process of producing rayon yarn and is a continuation inpart of my copending application Serial No. 122,367, filed January 26,1937. v a

It has for its objects improvement'in the efficiency of producing theseproducts, lessening the number of steps heretofore required, simplifyingthe installation of equipment-and its operation, lessening the number ofchemical elements required in the recovery processes and therebygenerally with the foregoing, cutting down the expense, producing agreen basic sulphate instead of a blue, thereby making it possible toproduce a thoroughly stable hydroxide, producing a dense crystalstructure susceptible to high concentration, and finally the effectingof economies in the utilization of the hydroxide in the production ofthe cupro-ammonium cellulose solution from which the fibres are spun, ajoint result of greater concentration and greater purity. The entireprincipal process is carried out at usual room temperatures eliminatingthe expense of heating enormous volumes of liquor.

One of the known types of processescommonly in use prior to my inventionis that of my "prior Patent No. 2,061,194 for Method of recoveringcopper from waste solutions, issued November 17, 1936, in which thewaste acid solution is passed in a continuous stream into a first tank,there agitated with sufiicient caustic soda to precipi tate to 75% asbasic copper sulphate, continuously overflowing the solution containingthe precipitate from the first tank into a second tank, there agitatingwith the addition of sufficient caustic soda to complete the copperprecipitation also as basic copper sulphate, overflowing the mixture ofthe second tank into a settling tank permitting it to settle, removingthe supernatant liquid therefrom, and finally removing the entireprecipitate from the settling tank in the form of a dense basic coppersulphate.

This basic copper sulphate was blue or a mixture of the blue and green,with the result that any attempt to produce copper hydroxide therefromwould have resulted in an unstable hydroxide in large part at least.,Furthermore, these coupled with other factors dictated the following ofthe old time practice of eiiecting immediate conversion into coppersulphate form, or treatment of basic copper sulphate with ammonia andammonium sulphate to form tetramine copper sulphate at such time as itwas desired to manufacture the cupro-ammonium' solution for spinning;Before the' solution was formed, it was :necessary to precipitate fromthe tetramine cop- .perhsulphate the copper in'the'form of copperdrawing-oh";

hydroxide, using for this purpose the full caustic equivalent ofthe'copper obtained. 1 All of these long steps oi-theold time processand. some of the chemical elements involved are eliminated by my newprocess. r 3 My new process in the-form'bes't'known to me at this timeis-carried out by continuously introducing the waste acid liquor duringa days' run into' a large tank and on alternate days using another largetank for this purpose, the size of these tanks being sumcient 'to holdthe waste acid liquorior a' full days run' of a given number of spinningunits. They are conveniently of approximately 50,000 gallons each. Notreatment is-given the'liquor introduced into these tanks during thetimefthe tank is filling to capacity. Of course, this might be'ajperiodeither less than or more than one day, theimportant thing being that thetank is large and that nothing is done until the-tank is filled. Whenthe one tank is a full, then the waste liquor is shifted to the otherand the liquor in the first is treated.

The treatment consistsin the immediate introduction of sufficientphosphoric acid or soluble phosphate to combine at proper acidity withthe iron contained to form ferric-phosphate' However, the iron 'remainsin solutionalong with the 'a'cid'until theproper acidity is obtained.'As the next ste'p'there is introduced sufficient caustic 'soda orits'equivalent to carry the acid toand below the point required forcombination of the iron and the phosphoric acid, and theferric-phosphat'e produced is precipitated to the bottom of the tank.Thereupon, the solution remaining above the precipitate is drawn out ofthetank so treated into a third tank which may or may not be empty, aswill laterbe-seen, at the time of n this third tank-the solution' drawnofffwhich contains iron' i'ree copper, is treated while the drawingisbeing done, and underconstant agitation with caustic soda su'fiicientto precipitate as.

basic copper sulphate 50 to 75% of the copper. At the time of startingsuch treatment during withdrawal, this thirdtank contains seed crystalsof green basic copper "sulphatejand through and Jay virtue of the factthat'it does cofitainjsuch crystals at the time-of starting, crystalsprecipitated during thecurrent treatment are also of 'green basic coppersulphate.

Seed crystals of green basic copper sulphate are produced originally inthis third tank through the treatment of a charge'drawn from one of thetwo initial receiving tanks containing iron free copper, by caustic sodaadministered in small dosages. This full third tank oi the solutioncontaining iron free copper' is given first a'dosage 'of caustic sodasufiicientto remove but 5 or-10% of the copper as'basic copper sulphate.A couple .of hours after the reactionpf the'first dosage of caustic sodaappears to have been complete, a second dosage of a like amount is givenand after a similar lapse of time a third dosage, and so on until enoughcaustic soda has been introduced to remove all that can be removed. Theinitial precipitate is a fine and faint green precipitate and grows moredense and more green with each dosage, until we have suitable green seedcrystals of large size and great density.

The green seed crystals having thus been formed and settled, thesupernatant liquid is withdrawn and the tank is ready for the continuousprocess as above set in motion.

As an alternative, instead of directly producing green seed crystals inthe treating tank I may produce them elsewhere and initially depositthem in the treating tank. They may be produced from blue basic coppersulphate crystals by boiling the blue crystals to remove the water ofcrystallization. duced in any precipitating tank merely by acidingsufiicient caustic soda to precipitate a major portion of the coppereither as the iron-free liquor is introduced, agitating the while, or bytreatment in bulk. In the treatment in bulk of course, it is importantto add the caustic with very great rapidity by reason of the bulkreaction desired. Whenever the caustic soda is in such high proportionthat the major portion of the copper is precipitated, the blue sulphatecrystals are precipitated. Thus if the precipitation by caustic soda issuflicient to deposit anywhere between 50 and 100% of the copper in asingle reaction, say specifically 80% or blue basic copper sulphatecrystals result. Boiling these then transforms them to green crystals.These after proper settling and flux of the precipitating tank may betransferred in suflicient quantity to any treating tank where it isdesired to produce the green crystals.

To return then to the discussion of the continuous processes, the liquidfrom the full tank containing iron-free copper, on the second andsucceeding days runs, is introduced into a third tank into which thesegreen crystals of basic copper sulphate are growing. The result of theintroduction of the caustic soda under agitation and suificient inquantity to precipitate 50 to 75% of the copper, is to precipitatecrystals of green basic sulphate and one other. Upon the third tanksbecoming filled with the iron-free copper solution, and thisprecipitation of 50 to 75% of the copper being complete, thereuponenough additional caustic soda is added to the now full tank toprecipitate the remaining copper, and this precipitate is likewise ofthe green basic sulphate. All of it is characterized by large grainsizes and great density.

The reaction being entirely complete, and sufficient time for thoroughsettling having been allowed, the supernatant liquid of this third tankis withdrawn and carried away. Thereupon, the precipitate of green basicsulphate, if there has been accumulation sufficient to justifywithdrawal, is withdrawn and subjected to the addition of caustic sodain such amount as to completely convert it into what now is of necessitya stable copper hydroxide by reason of the fact that we are dealing withthe green copper sulphate and not with the blue. The soda content of thecaustic combines with the sulphate radical and the resultant sodiumsulphate is removed by washing. It may require, according to the size ofthe tanks used, several days to accumulate sufficient precipitate tojustify withdrawal and The blue can be proconversion into hydroxide.With the 50,000 gallon size, three or four days or some times a weeksaccumulation is allowed before Withdrawal of the precipitate from thethird tank. However, there is always left in the tank a sufficientquantity of seed crystals of the green basic sulphate to assureresumption of the process when solution containing iron-free copperagain is drawn from the initial receiving tanks. Each day, at the end ofthe treatment in this precipitating tank, the supernatant liquid is ofcourse withdrawn, except for such portion as renders the sulphatesufficiently liquid to be stirred and pumped.

The initial receiving tanks used on alternate days are permitted toretain precipitation of ferric-phosphate for a number of days, sincethis is not very great and may be removed at intervals of one or twoweeks or more, since the mere fact that these initial receiving taks areused alternately extends the time during which the removal ofprecipitate ferric-phosphate is made.

As stated at the beginning of this specification this copper hydroxideproduced from the green basic copper sulphate is characterized by anessential and maintained stability as distinguished from an outstandinginstability possessed by that copper hydrozn'de produced from the bluebasic sulphate by caustic conversion. The unstable hydroxide producedfrom the basic blue copper sulphate, on account of the impuritiesresulting from its instability (largely copper oxide) is antagonistic tothe attainment of maximum solvency of cellulose when the hydroxide isadmixed with ammonia for the making of the cuproammonium cellulosespinning solution. The hydroxide produced by direct application ofcaustic from the green basic copper sulphate being thoroughly stablesets up none of these compounds which decrease its solvent action andenables me toattain the highest efliciency in producing by means of it acupro-ammonium cellulose spinning solution.

I do not know certainly the reasons for this instability of thehydroxide derived from the blue crystals, but I believe them to be atleast inelusive of the fact that the blue basic copper sulphate crystalcarries water of crystallization (about two molecules) and that thepresence of this water of crystallization may be continued in some partin the resultant copper hydroxide. This apparently makes for an unstablestructure, the copper hydroxide tending to lose its water of compositionand change partly to copper oxide (CuO). The color thereby changes frombright pure blue to something ranging from light brown to black,depending on the extent of loss 01' water of composition. The molecularcompositions of the blue and green basic sulphates are as follows:

Blue: 3Cl.1( OH) 2.Cl1SO4-I2H2O Green: 3Cu(OI-I) 2.CuSO4 with causticsoda and by the expression green basic copper sulphate as used in theclaims,rI mean a basic copper sulphate of such color which containssubstantially no water of crystallization such as occurs in a definitemolecular ratio and in which the molecular ratio of copper hydroxide tocopper sulphate is substantially three to one. Yet further advantageaccrues from the use of my process in that I have introduced as a stepof this process the removal of the iron and other impurities by thephosphate treatment according to my patent application Serial No.103,910 filed October 3, 1936. By removing these impurities beforeresolution of the copper into solid compounds I prevent any part ofthese impurities, particularly the iron, from following the copper anyfurther than the first stage of treatment. Before this invention in somesituations one was confronted not only with inefficiency of solventaction and impurity of the resultant cupro-ammonium spinning solutiondueto the compounds resulting from instability, but also with weakeningof the solvent action by impurity due to the presence of the iron andother foreign substances. It was possible in the old process to get ridof the iron and other foreign substances by filtration at the properstage, but this process of riddance was cumbersome and expensive.

Finally the stable copper hydroxide so produced is characterized bylarge grain size and high density. This affords directly the highconcentration so largely desirable in the preparation of theoupro-ammonium cellulose mixture or goo, because the copper hydroxidemust be added in the form of a water suspension and is capable of higherconcentration the larger and denser the grain. The higher theconcentration the less will be the dilution of the ammonia used in makinthe goo. The large grain size and high density thus facilitates themaking of a very concentrated goo as described in my earlier U. S.Patent No. 2,061,194 issued November *7, 1936 and U. S. [Patent No.2,047,466 issued July 14, 1936 to William Henry Furness.

Viewed in these lights, the high merit in the initial removal ofimpurities and the direct precipitation of green basic copper sulphateunder caustic treatment should be fully apparent. The process is notonly simplified in the number of chemicals and number of steps required,but is itself more efiicient, and on top of that renders the productionof the spinning solution simultaneously less expensive and moreefficient.

The modifications of which my invention is susceptible and the variedapplications are quite as great in number as those usually met with.

In the first place, I would point out that in the treatment to removethe foreign iron in the initial receiving tanks, the amounts of acid andcaustic may both be varied to points in excess of amounts required forthe reactions desired. Such modification is always a good rule andresults in a certainty of complete reactions which cannot otherwise beobtained. In the second phase of my invention, the treatment in theprecipitating tank for basic copper sulphate, I have given an initialmeasure of caustic soda to be used as that sufiicient to precipitate 50to 75% of the copper. This may be decreased or increased, and I haveused a percentage as high as 90 to 95. However, I desire to keep underthat quantity necessary to precipitate 100% of the copper for the reasonthat green basic copper sulphate is more surely formed, and sufiicienttime of reaction is more fully guaranteed when the precipitation takesplace in a solution more iully acid.

Once the seed body of green crystals is formed in the tank it isfeasible for me to treat the day's run removed from the ironprecipitating tank either as it is removed or in bulk. This is for thereason that the body of seed crystals which I maintain at all timeswithin the treating tank is several times greater than the amount ofgreen seed crystals obtained by treating the liquor of a days run. I maymake this proportion as low as 3 or as high as 10, and especially whenthe proportion is higher, bulktreatment may be resorted to, the causticbeing added in the same rate per minute as during partial or progressiveprocessing. A convenient and efficient mode is a combination of the bulkand partial or progressive treatments. According to this mode I permitthe treating tank to fill to one-half its capacity with the. iron-freedliquor and then commence the addition of alkali in the proportions givenfor the tank in which the body of seed crystals has been grown.

At the end of the days run, the precipitation having been complete, thesupernatant liquor is drawn off not wholly but leaving a residuesufiicient to be admixed with the precipitated green crystals byagitation and permit them to be pumped off. Always there would be leftinthe tank a quantity of seed crystals several times that precipitatedfrom, a full tank charge, whether the full tank charge be that of onedays run or some fraction thereof.

My process may be modified by deliberately producing the blue basiccopper sulphate crystals in bulk and the changing them in bulk to greenwhich in turn I convert directly into stable copper hydroxide. thatheretofore described. Thus I would flow the liquor from the storage tankin which the iron is precipitated not into a green seed crystal tank,but into a blue seed crystal tank of sufficient capacity to treat inbulk by the method just now described to produce the blue crystals. Thisliquor having been converted by this process of precipitation" of themajor proportion of the copper in the presence of blue seed crystals,into blue basic copper sulphate, periodically the blue basic coppersulphate crystals would be withdrawn to yet another tank and thereheated in bulk to remove the water of crystallization and convert themas a whole into green basic'copper sulphate. This is all without anygrowing of green seed crystals. The green bulk crystals so produced arethentreated as described hereinafter to convert into copper hydroxide.

This process, however, is not so efficient as that which I havedescribed in principal place, the direct conversion of the iron freeliquor into green basic 'c'opper sulphate, in that heat is required forthe conversion of blue crystals and this heat as applied to therelatively large quantities to be treated in a modern rayon plantinvolves appreciable added expense. The expense is also added toslightly by the added cost of added equipment and slight additionallabor.

Further, it must be quite apparent that alkali other than caustic sodamay be used. There are several well known to be suitable in connectionwith such processes, for example, ammonia, sodium carbonate, etc.

A dilute waste acid liquor commonly treated by my method and itsmodifications to recover the copper is the following: One containingThis is a modified method to I amounts.

The presence of the ammonia salt is very favorable to the process. Itspresence is an important factor in the attainment of the greater densityand grain size of the green basic sulphate and the resultant density andconcentration of the copper hydroxide, and, in practice, I have found itdesirable to add sufficient fresh ammonia sulphate to the solution toraise the percent content to of one percent.

There are a number of such solutions. In some of them the ammonia saltmay be absent. In such case I would propose to treat the Waste liqnorwith ammonia instead of caustic, thereby cutting down the volume of theprecipitate and improving its grain size and compactness, therebyaifording the direct concentration of the copper hydroxide producedwhich I desire Without special treatment.

What I claim is:

1. The method of producing stable copper hydroxide which comprises firsttreating a quantity of dilute cold copper sulphate solution byadministering a plurality of small dosages of an alkali, at intervalsspaced substantially by the reaction time for each dosage to cause thegrowth of green basic copper sulphate crystals for seed purposes,drawing off the supernatant liquid, secondly adding fresh dilute coldcopper sulphate solution while adding an alkali at a rate insufficientto precipitate all of the copper sulphate in the form of green crystals,adding to such solution containing precipitated crystals, sufficientadditional alkali to precipitate the remaining copper sulphate in theform of green crystals, drawing off the supernatant liquid, re-

peating said second named series of steps, said method being carried outwithout application of heat from external sources, removing only aportion of said green crystals from time to time as the growth warrantsbut retaining a substantial portion for seed purposes, and treating theremoved green crystals with an alkali to produce stable copperhydroxide.

2. The method of producing stable copper hydroxide which comprises firsttreating a quantity of dilute cold copper sulphate solution containingan ammonium salt by administering a plurality of small dosages of analkali, at intervals spaced substantially by the reaction time for eachdosage to cause the growth of green basic copper sulphate crystals forseed purposes, drawing off the supernatant liquid, secondly adding freshdilute cold copper sulphate solution likewise containing an ammoniumsalt while adding an alkali at a rate insufiicient to precipitate all ofthe copper sulphate in the form of green crystals, adding to suchsolution containing the precipitated crystals, sufiicient additionalalkali to precipitate the remaining copper sulphate in the form of greencrystals, drawing oil the supernatant liquid, repeating said secondnamed series of steps, said method being carried out without applicationof heat from external sources, removing only a portion of said greencrystals from time to time as the growth Warrants but retaining asubstantial portion for seed purposes, and treating the removed greencrystals with an alkali to produce stable copper hydroxide.

3. The method of producing stable copper hydroxide which comprisesflowing a quantity of dilute cold copper sulphate solution into a bathcontaining a quantity of green basic copper sulphate seed crystals whileadding an alkali at a iron,'silica, and aluminum in small and varyingrate insufiicient' to precipitate all ofthe copper sulphate in the formof similar green crystals, thereafter adding to such solution containingprecipitated crystals, sufficient additional alkali to precipitate theremaining copper sulphate in the form of green crystals, drawing off thesupernatant liquid, repeating said process, said method beingrcarriedout without application of heat from external sources, removing only aportion of said green crystals as the growth warrants, but retaining asubstantial portion for seed purposes, and treating the removed greencrystals with an alkali to produce stable copper hydroxide.

4. The method of producing stable copper hydroxide which comprisesflowing a quantity of ,dilute cold copper sulphate solution containingan ammonium salt into a bath containing a quantity of green basic coppersulphate seed crystals while adding an alkali at a rate insufiicient toprecipitate all of the copper sulphate in the form of similar greencrystals, thereafter adding to such solution containing precipitatedcrystals, sufiicient additional alkali to precipitate the remainingcopper sulphate in the form of green crystals, drawing off thesupernatant liquid, repeating said process, said method being carriedout without application of heat from external sources, removing only aportion of said green crystals as the growth warrants, but retainingasubstanti'al portion for seed purposes, and treating the removed greencrystals with an alkali to produce stable copper hydroxide.

5. The method of producing green basic copper sulphat'e'from dilute coldwaste acid liquor derived from the treatment of the coagulated fibre ofthe cupro-ammonium process of producing rayon yarn, which consists infirst treating a quantity of the liquor to free it of iron content,progressing the iron free solution to a container having seed crystalsof green basic copper sulphate, while adding an alkali to the solutionat a rate insufficient to precipitate all of the copper sulphate,thereafter adding to the container enough alkali to complete theprecipitation of the remaining copper sulphate in the form of greencrystals, said method being carried out without application of heat fromexternal sources.

6. The method of producing stable copper hydroxide from green basiccopper sulphate from'dilute cold waste acid liquor derived from thetreatment of the coagulated fibre of the cupro-ammonium process ofproducing rayon yarn, which consists in first treating a quantity of theliquor to free it of iron content, progressing the iron free solution toa container having seed crystals of green basic copper sulphate,whileadding an alkali to the solution at a rate insuflifcient toprecipitate all of the copper sulphate, thereafter adding to thecontainer enough alkali to complete the precipitation of the repersulphate from the waste acid liquor derived from the treatment of thecoagulated fibre of the cupro-ammonium process of producing rayon yarn,which consists in first substantially freeing the liquor of its ironcontent, progressing the solution freed from the iron to a region remotefrom the region of the iron removal and char- 7? acterized by thepresence of seed crystals of green basic copper sulphate, and in thislatter region at ordinary temperature treating the progressed solutionunder constant agitation with an alkali added at a rate less than thatwhich will tend to precipitate crystals of blue basic copper sulphate inthe presence of the seed crystals of green basic copper sulphate.

8. The method of producing green basic copper sulphate from the wasteacid liquor derived from the treatment of the coagulated fibre of thecupro-amrnonium process of producing rayon yarn without substantialheating which consists in precipitating green basic copper sulphate inthe presence of green basic copper sulphate seed crystals by alkalitreatment and in which the alkali applied in the region of the seedcrystals of green basic copper sulphate is applied in sufiicientquantity to precipitate as green basic copper sulphate 50 to of thecopper of the sollution as it is progressively drawn into this regionand when the drawing in of the copper solution is completed bycontinuing the addition of alkali until all remaining copper from thesolution is precipitated likewise in the form of green basic sulphate,said method being carried out without application of heat from externalsources.

9. Process according to claim 7 in which the seed crystals aremaintained in quantity manifoldly greater than the quantity producedduring the period of precipitation.

10. Process according to claim '7 in which the seed crystals of greenbasic copper sulphate are produced initially by alkali treatment of theiron free solution in stages, precipitating but a few per cent of thecopper at a time from the solution, thereby gradually building up a bodyof green seed crystals.

11. A process according to claim 7 in which the seed crystals of greenbasic copper sulphate are initially produced by first growing blue basiccopper sulphate crystals, by rapid alkali treatment of an iron-freewaste liquor solution to precipitate the copper carried in the solutionand thereafter heating suifi'ciently to drive out the water ofcrystallization to transform. the blue basic sulphate crystals intogreen basic sulphate crystals.

12. The method of producing green basic copper sulphate which comprisesfirst treating a quantity of dilute, cold copper suphate solutioncontaining an ammonium salt, by administering a plurality of smalldosages of an alkali at intervals spaced substantially by the reactiontime for each dosage to cause the growth of green basic copper sulphatecrystals for seed purposes, drawing off the supernatant liquid, secondlyadding fresh dilute cold copper sulphate solution likewise containing anammonium salt while adding an alkali at a rate insuflicient toprecipitate all of the copper sulphate in the form of green crystals,adding to such solution containing the precipitated crystals, sufficientadditional alkali to precipitate the remaining copper sulphate in theform of green crystals, drawing off the supernatant liquid, repeatingsaid second named series of steps, removing only a portion of said greencrystals from time to time as the growth warrants but vretaining asubstantial portion for seed purposes, said method being carried outwithout application of heat from external sources.

13. The method of producing green basic copper sulphate which comprisestreating a quantity of dilute, cold copper sulphate solution having asmall percentage of an ammonium salt, by administering a plurality ofsmall dosages of an alkali at intervals spaced substantially by thereaction time for each dosage to cause the growth of green basic coppersulphate crystal for seed purposes, drawing off the supernatant liquid,thereafter adding fresh dilute cold copper sulphate solution, andthereafter adding alkali at a rate slow enough to insure the formationof green crystals only, said method being carried out withoutapplication of heat from external sources.

14. Method of producing at ordinary temperatures green basic coppersulphate from copper sulphate in a solution which consists inintroducing a determinate bulk of the copper sulphate solution to thepresence of green basic copper sulphate seed crystals of sufficientquantity to substantially influence the precipitation of furthercrystals of green basic copper sulphate upon the introduction of analkali, introducing an alkali at a rate substantially less than thatwhich tends to produce blue basic copper sulphate, and continuing theintroduction of the alkali until substantially all the copper of theentire bulk of copper sulphate solution has been precipitated out asgreen basic copper sulphate, the solution being agitated throughout theprocess, said method being carried out without application of heat fromexternal sources.

15. Process according to claim 14 in which the seed crystals of greenbasic copper sulphate are produced by first placing the bulk of thecopper sulphate in solution in the same region where the seed crystalsare desired, introducing the alkali in stages such as to precipitate buta few per cent of the copper in each stage as green basic coppersulphate crystals, thereby gradually building up the body of green seedcrystals, permitting the seed crystals to settle, drawing off the liquorand thereupon continuing the process according to claim 14. I

16. Method according to claim 14 in which th seed crystals of greenbasic copper sulphate are produced initially from cold copper. sulphatesolution having a small percentage of ammonium salt, by administering aplurality of small dosages of an alkali at intervals spacedsubstantially by the reaction time for each dosage to cause the growthof green basic copper sulphate crystal for seed purposes, and drawingoff the supernatant liquid.

17. The method of producing green basic copper sulphate from the wasteacid liquor derived from the treatment of the coagulated fibre of thecupro-ammonium process of producing rayon yarn, said method beingcarried out Without application of heat from external'sources, whichconsists in precipitating green basic copper sul' phate in the presenceof green basic copper sulphate seed crystals by alkali treatment and inwhich the alkali applied in the region of the seed crystals of greenbasic copper sulphate is applied at a rate'less than than which willtend to precipitate crystals of blue basic copper sulphate in thepresence of seed crystals of the greenbasic copper sulphate.

SVERRE GULBRANDSEN.

